1. Field of the Invention
The present invention relates to a parameter extraction method for elements having a plurality of parameters, and to a computer readable storage medium containing a program executing the parameter extraction method. In particular, the present invention relates to a parameter extraction method for semiconductor circuit simulation in designing semiconductor circuits, in which behaviors of designed circuits are verified by assigning parameters describing behaviors of circuit components using model equations for semiconductor elements, and further relates to a computer readable storage medium containing a program executing the parameter extraction method.
2. Description of the Related Art
In general, circuit simulation is performed to verify operations of a circuit by directly inputting conditions required for circuit simulation, such as circuit connections, element model parameters, analysis conditions, output conditions; or by indirectly using the data of input information.
The element model parameters of the input information are physical parameters or semiempirically determined parameters, which are included in an analytic expression in which an input-output response characteristics of an element is modeled. As an example of MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) models, a BSIM3 model or the like can be used. BSIM3 is a model generally called a SPICE (Simulation Program with Integrated Circuit Emphasis) model, which reproduces an input-output responses of elements on a SPICE-based circuit simulator commonly used for circuit simulation. BSIM3 is made to require less calculation because it is used for calculations handling behaviors of as many as several ten thousands or more elements at a time.
Instead of using element model parameters, a method of reproducing behaviors of an element by a device simulation device may be used to perform circuit simulation. However, when a device simulation device is used in combination with a circuit simulation device, the scale of analysis becomes larger at the cost of higher analytical accuracy; besides, speed of analysis is reduced accordingly. Therefore, it is not practical to use a device simulation device, which is rarely used.
As a result, when simulation of a large-scale circuit is performed, generally, behaviors of elements forming a circuit are described using model equations and model parameters of the elements to perform circuit simulation by processing the information on model equations and the element model parameters using a circuit simulation device. In this case, if device characteristics reproduced from the model equations and the element model parameters do not fully match the characteristics of the elements forming the circuit, the simulation result of the circuit does not agree with an analysis result of a circuit actually formed.
In order to verify circuit operation with high accuracy, at the element level, it is necessary to determine element model parameters appropriately. As criteria of whether the element model parameters are appropriate or not, the difference between measured characteristics of an element (hereinafter referred to as measured characteristics) and calculated values based on an analytical model (hereinafter referred to as virtual characteristics)(hereinafter also referred to simply as error) is used. Element model parameters are combined so as to ideally minimize this error, and the difference is used to verify circuit operation; thus, highly accurate verification can be performed. Determining a combination of model parameters used for verifying circuit operation is referred to as parameter extraction.
Further, with respect to a method for efficiently extracting parameters regarding behaviors of elements forming a circuit, for example, Reference 1 (Japanese Published Patent Application No. 2001-148333) discloses a technique in which a solution such as Newton's method or a variant thereof is implemented to minimize the difference between a measured value and a calculated value to find approximations to the true value.